Conventionally, as a power plant of this kind, there has been known one disclosed e.g. in PTL 1. In this power plant, a differential gear unit including first to fourth rotary elements is formed by combining first and second planetary gear units of a so-called single planetary type with each other. The rotational speeds of the first to fourth rotary elements satisfy a collinear relationship in which the rotational speeds are aligned in a single straight line in a collinear chart. Specifically, the first planetary gear unit includes a first sun gear, a first carrier, and a first ring gear, and the second planetary gear unit includes a second sun gear, a second carrier, and a second ring gear. The first sun gear and the second carrier are connected to each other via a hollow cylindrical first rotating shaft, and the first carrier and the second sun gear are connected to each other via a solid second rotating shaft. The second rotating shaft is rotatably disposed inward of the first rotating shaft.
In the differential gear unit constructed as above, the first ring gear corresponds to the first rotary element, the first carrier and the second sun gear connected to each other correspond to the second rotary element, the first sun gear and the second carrier connected to each other correspond to the third rotary element, and the second ring gear corresponds to the fourth rotary element. Further, this conventional power plant is installed on a four-wheel vehicle, with the first rotary element connected to a first rotating electric machine, the second rotary element connected to a left drive wheel, the third rotary element connected to a right drive wheel, and the fourth rotary element connected to a second rotating electric machine. In the power plant, by controlling the first and second rotating electric machines, torque distributed to the left and right drive wheels is controlled.
Further, as the conventional power plant of the above-described kind, there has been known one disclosed e.g. in PTL 2. This conventional power plant is formed by combining first to third planetary gear units of the single planetary type with each other, and includes first to fifth elements that can transmit motive power therebetween. As shown in FIG. 88, these first to fifth elements are configured such that the rotational speeds thereof satisfy a collinear relationship, and in a collinear chart representing the collinear relationship, the rotational speeds of the first to fifth elements are aligned in a single straight line, in the mentioned order. Specifically, the first planetary gear unit includes a first sun gear, a first carrier, and a first ring gear, and the second planetary gear unit includes a second sun gear, a second carrier, and a second ring gear. The third planetary gear unit includes a third sun gear, a third carrier, and a third ring gear. The first carrier and the third ring gear are integrally connected to each other, the third carrier and the first and second ring gears are integrally connected to each other, and the second carrier and the third sun gear are integrally connected to each other, whereby the above-described first to fifth elements are formed.
Further, the conventional power plant is installed on a four-wheel vehicle, with the first element connected to a first rotating electric machine, the second element connected to a left drive wheel, the third element connected to an engine, the fourth element connected to a right drive wheel, and the fifth element connected to a second rotating electric machine. By controlling the first and second rotating electric machines, torque distributed to the left and right drive wheels is controlled.